The organization and expression of genes involved in siderophore-mediated iron transport in the corn smut pathogen Ustilago maydis will be examined. The importance of this system to the virulence of the fungus will also be assessed. The specific aims of this proposal are: (1) to isolate and genetically and biochemically characterize mutants of U. maydis that are defective in the biosynthesis and utilization of the siderophores ferrichrome and ferrichrome A; (2) to develop an efficient gene transfer system for U. maydis; (3) to clone the genes for the production and transport of the siderophores; (4) to study the structure and organization of these genes; (5) to analyze siderophore gene expression; and (6) to assess the role of siderophores in the pathogenicity of U. maydis. These experiments involve natural products chemistry, enzymatic assay, gene cloning, nucleic acid hybridization, restriction mapping, DNA sequencing, in vitro site-specific and deletion mutagenesis, and genetic analysis. Knowledge gained from these studies would provide a fundamental understanding of the biochemistry and molecular biology of iron transport in a eucaryotic system.